The present invention relates to a magnetic head assembly for the recording and reproducing of information signals, and more particularly to a magnetic head assembly of this kind for use in a flexible disc apparatus handling a flexible recording medium, which is suitable for obtaining a stable contact condition between the medium and the magnetic head and for greatly reducing the risk of damage to the medium.
A conventional flexible disc driving apparatus shown in FIG. 1 has a magnetic head assembly 1 which contains magnetic heads and is supported by guide rails 2. The apparatus is constructed so that the assembly 1 is movable in the radial direction (in the direction indicated by arrows (A) of a disc 3 and relative thereto by the operation of a stepping motor 5, through a pulley mounted on the end of the motor 5 and a band 7 wound around the pulley 6. The disc 3 has tracks 4 for recording information in a concentric manner.
In the above apparatus, information signals are magnetically recorded on the tracks 4 of the disc 3 (by magnetization inversion recording) in the following manner: the disc 3 is rotated by a motor (not shown in the drawing) in the direction indicated by the arrow B; the magnetic head is moved to a desired track on the disc 3; and the magnetic head is pressed against the disc 3, thereby performing recording.
The reading (reproduction) of the thus-recorded information is carried out by obtaining information signals which have been magnetically recorded on the disc 3 in the form of voltages induced in coils arranged in the magnetic heads. It is well known to carry out reproduction in this manner, so specific illustration of this operation will be omitted.
The magnetic head 13a, 13b serves as a converter which performs the recording or reproduction of the information. FIG. 2 shows a section through the entire structure of the magnetic head assembly.
Referring to FIG. 2, a slider 12a, in which a core (an element corresponding to that indicated by reference number 25a or 25b in FIG. 4) and a winding of a magnetic head are embedded, is mounted on a swing arm 9a by being elastically supported by a gimbal 11a and a load-spring 10a. The swing arm 9a is supported by a support spring 16a on a carriage 8 forming a main body of the magnetic head assembly and is urged toward a stopper portion 8a provided at the end of the carriage 8 by a pressure-spring 14a. A second slider 12b in which a core and a winding of a magnetic head are embedded, has substantially the same structure as that of the first slider 12a, except that the second slider 12b is additionally provided with a hook 20 formed on a swing arm 9b. The swing arms 9a and 9b are provided with cams 19a and 19b, respectively, and their design is such that, when the hook 20 is lifted, the swing arms 9a and 9b are opened by the cams 19a and 19b, thus providing a gap between the sliders 12a and 12b. This design ensures that the disc 3 and a jacket (an element corresponding to that generically indicated by reference number 23 in FIG. 4 hereinafter referred to) of the flexible disc cartridge can be inserted into the gap between the sliders 12a and 12b.
FIG. 3 shows the structure of the swing arm 9b. Reference numbers in FIG. 3 indicate the same elements as those shown in FIG. 2, and a detailed explanation of the elements will be omitted.
The conventional magnetic head assembly having the structure described above suffers from the following problems when a flexible disc cartridge is mounted therein in operation. FIG. 4 is a view showing the magnetic head sliders 12a and 12b in an example of the state in which they are pressed against the disc 3, taken from the center of the disc 3 shown in FIG. 1. In FIG. 4, the symbol H represents the height of a level 102, at which the sliders 12a and 12b are in contact with each other, above the center of the guide rails 2. The symbol h represents the dimension between the center of the guide rails 2 of the chassis on which the magnetic head assembly 1 and the stepping motor 5 are mounted and a reference level 21 at the lower surface of a jacket sheet 23a pressed against another jacket sheet 23b via the disc 3, as shown in the lefthand side of FIG. 4. The reference level 21 is used as a reference for determining the position of the disc 3. The symbol t represents the sum of thicknesses of the jacket sheet 23a and a liner 24a. The difference .DELTA.H between the height H of the contact level 102 between the sliders 12a and 12b and the height of the lower surface of the disc 3 (the height above the reference level 21 of which is equal to the thickness t), respectively measured from the center 2a of the guide rails 2, can be expressed by the following equation (1): EQU .DELTA.H=H(h+t) (1)
This difference .DELTA.H is called the head penetration, and, in general, it should preferably have a value within the range of 0.2 to 0.3 mm. However, in the structure of the magnetic head shown in FIG. 2, since the sliders 12a and 12b are pressured by the load-springs 10a and 10b respectively, the position of the contact level 102 between the sliders 12a and 12b is balanced at a position which varies with the balance between the urging forces of the load-springs 10a and 10b. This means that it is difficult to obtain a prescribed dimension, i.e., the above-mentioned height H, of the contact level 102, unless the forces of the load-springs 10a and 10b are made to be exactly the same as each other in their manufacture. Therefore, as shown in FIGS. 5(a) and 5(b), deviations in the height of the contact level 102 occur. More specifically, a deviation in a height Ha from the prescribed dimension H by an amount .delta.a as shown in FIG. 5(a), or a deviation in a height Hb therefrom by an amount .delta.b, as shown in FIG. 5(b), occurs. This deviation amount 6a or 6b means that the difference .DELTA.H can not always be brought within the above generally-preferred range of 0.2 to 0.3 mm. As a result, the head penetration becomes excessive (because of the amount .delta.a) or insufficient (because of the amount .delta.b), causing unstable contact between the magnetic head cores 25a and 25b and the disc 3 with slight gaps intervening. This leads to the problem of a significant deterioration in the recording characteristics of the apparatus. More specifically, although, as shown in FIG. 6(a), the reproduction output should have a constant, flat envelope of amplitude (shown in terms of voltage in FIGS. 6(a) to (c)) of its reproduced signals, short-term oscillations (indicated by reference number 26 in FIG. 6(b), partial drops (indicated by reference number 27 in FIG. 6(b)), or drops in the reproduction output (shown at 28 in FIG. 6(c)) can occur, reducing the reliability of the apparatus in the recording of information signals. In addition, because of the unstable contact between the cores 25a and 25b and the disc 3, the contact between the sliders 12a and 12b and the disc 3 also becomes unstable, often leading to another problem concerning damage to the disc 3.
U.S. Pat. No. 4,089,029 and Japanese Patent Laid-Open No. 51-124910 disclose conventional known magnetic head assemblies of the type described above.